Shielded mica spark plug



Feb. 23, 1937. H. RABEZZANA SHIELDED MICA SPARK PLUG Filed Feb. 14, 1935 Kdezzarza Patented Feb. 23, 1937 UNITED STATES SHIELDED MICA SPARK PLUG Hector Rabezzana, Flint, Mich., assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Application February 14, 1935, Serial No. 6,455 I 7 Claims.

My invention relates to spark plugs for internal combustion engines; and the object thereof is to provide improved shielding means for preventing the high tension current supplied to a spark plug from interfering with the proper operation of radio apparatus located adjacent the engine, in airplane and similar service wherein radio apparatus is used. This is accomplished by the use of a metallic sheath surrounding the high tension supply conductor whereby current is supplied to the plug, which sheath is grounded upon the external metallic casing of the plug and which casing, being screwed into a threaded opening in the engine head, is in turn grounded upon the engine; whereby electrical waves of high frequency eman'atingfrom the ignition system of the engine are grounded thereupon and are prevented from reaching adjacent radio sending and receiving apparatus.

A further object of my invention is to provide for more complete and effective cooling of spark plugs used in internal combustion engines wherein compression of the combustible mixture before ignition thereof, is inordinately high, as is commonly the case in engines used with airplanes. Such high compression, in connection with the fact that suchengines are often if not usually air cooled engines, results in the subjecting of the plugs to much higher temperatures than is the case where the engines operate at lower and more normal temperatures and high plug temperatures are likeLv to cause pre-ignition of the combustible mixture. This is avoided in'plugs made in accordance with my invention by particular features of plug construction and arrangement of parts which are conducive to the operation thereof at a lower temperature than would otherwise be the case, and by' providing the plu with heat radiating devices designed to secure a rapid dissipation of such heat as reaches the plug to the head of the engine cylinder and to the surrounding atmosphere.

The preferred form of my invention is illustrated in the accompanying drawing, and the particular features wherein the same consists are enumerated in the claims at the end of this specification.

In the drawing:

Figure l is a view showing 'a section upon a central plane, of a spark plug and associated shielding and cooling means made in accordance with my invention.

Figure 3 is a sectional view similar to Figure 1 but showing another form of my invention.

Figure 4 is a. view showing a section upon a transverse plane indicated by the line 4-4, Figure 3, looking down. 5

Figure 5 is a fragmentary sectional view showing a. modified form of cooling member usable in lieu of the cooling member shown in Figure 1.

Referring now to the drawing, the numeral 6 designates the external metallic shell or casing 10 'of a spark plug made in accordance with my invention and which is threaded as shown to screw into a spark plug opening in the head of an internal combustion engine, whereby the shell becomes grounded. The shell has the usual 15 grounded or shell electrode 1; and the upper end thereof is internally threaded to receive the lower end of a tubular metallic gland nut and shield member 8 which is obviously grounded upon the shell, and which extends above the shell or casin 20 of the plug. This gland nut and shield member forms a support for the central insulated electrode 9 of the plug and both are readily removable from the shell 6 because of the threaded connection between them; the said member, the 25 insulating means whereby the central electrode is insulated therefrom, and the electrode itself, forming a single unitary assembly removable from and replaceable within the shell or casing of the plug. The support for the central electrode may, 30 however, be permanently assembled with the shell as in so-called single piece spark plugs.

The main body part of the central electrode 9 may be made of any suitable steel and, while the head Illand tip thereof may be of the same 5 material as the body, these parts are preferably made of materials selected with the end in view of better resisting the'action of high temperature gases inside the engine cylinder and the action of sparks passing between the tip and the ground- 40 ed electrode, in which case the several parts of the electrode are welded together to form an integral structure. However and whatever mate-\ rial the electrode 9 may be made of it is provided with an outer tubular covering I! of copper 45 to secure better conduction of heat away from the head ill and tip I I and the upper end of said electrode terminates, as shown in the drawing, slightly above the upper end of the shell 6; so that, so far as the central electrode is concerned, the 50 good low resistance path for the flow of heat away from its lower end of the electrode ends at or slightly above the upper end of the shell 6. Heat reaching the upper end of the electrode then flows through the tubular insulating member I! sur-,

rounding the electrode and to the shield member 8, and therefrom partly to the casing. of the plug and partly. to the surrounding atmosphere;

Surrounding thecentral electrode 9 and extending from the head ID thereof beyond the upper end of the shell 6, and terminating adjacent the upper end of the gland nut and shield member 8, is a tubular insulating member 3 made of sheet 'micaand which member extends through a metallic sleeve M which fits Within a seat formed within the gland nutpart of said member 8; the

direct contact with'the interior vof the. passage along which it extends. Said sleeve I4 is made to grasp the exterior .of the tubular insulating nut and shield member 8, as shown at 26 and 21,

member l3 and compress the same agai'nst'the' central electrode 9 to therebyhold the same in assembled relation with the gland nut and shield member 8; and an inner insulating member |5 made up of mi'cadiscs or washers surrounds the lower end of said tubular insulator and 'lies between the upper side of the head |u and the lower end of the sleeve l4.

The numerals |6, designate a twopart 'me-' tallic terminalconnector casing which is detachably secured to the upper end of the gland nut and shield member .8 through a flange-and by atubular nut l8 'whereby said casing is grounded, and within which casing is an insulator 9 moulded to fit inside the same and which may be made of any suitable insulating material. The inner part 20 of this insulator extends-into the tubular insulating member |3 to a point-adjacent. the upper end of the central electrode 9, and the outer part 2| thereof is tubular inform to receive the end of a supply cable 22 for supplying high tension current to the central electrode. This supply conductor has an insulating covering 23 of rubber or equivalent material, and the same isenclosed within a metallic sheath 24 which is fastened .to the casing through a flange and by a tubular nut 25 whereby said sheath is grounded as will be understood. Suitable yieldable gaskets are provided between the flange at the end of the sheath '24 and .the adjacent end of the casing sec- 7 tion l1, and between the flange at the end of the casing section IB'and the-upper end of the gland Figure 1. v x

Enclosed within the moulded' insulator l9 as by being embedded therein is a wire 28 whereby a current conducting path is provided between the supply cable 22 and the upper end of the central electrode 9, and the diameter of which wire is as small as it may be conveniently made so as to prevent, as. much as possible, the conduction of heat to the supply cable and injury, by excessive heating thereof, to the rubber composition insulation 23 thereof. 'For convenience in establishing connections with the ends of this wire one end thereof is connected. with a terminal 29 located within the insulator l9, and which terminal is grasped by a resilient clasp 30 secured to the end of the supply cable 22; and the other end thereof is connected with'a second terminal or disc 3| at the lower end of the depending part 20,0f said .insulator. A spring 32 is supported upon the upper end of the electrode 9 and the upper end thereof contacts with the disc 3| whereby a conthe wire 28.

nection is established with the electrode when the depending part 20 of the insulator is entered into the tubular insulating member l3, and the curved part l6 of the terminal connecter casing is secured to the upper end of the gland nut and shield member 8 by the tubular nut [8. I a

It therefore follows thatthe gland nut and shield member 8, the insulator casing I6, l1, and the metallic'sheath 24 are grounded upon heated head ID and terminal flows freely along the copper covering l2 of the central electrode to the upper ends of said parts at which point the I heat conducting path is interrupted, and the greater part of the heat flows through'the tubular insulating member l3 and to the sleeve 14, and

from it to the gland nut part of the gland nut I and shield member 8 and to the shell 6 and .to

the cylinder head. Such heat as flows along the gland nut and shield member. 8 is dissipated by the terminal connecter casing parts l6, I! which are directly exposed to the surrounding atmosphere; and littleior no heat will flow along the wlre 28 to the insulating covering 23 of the supply cable 22. Furthermore and because the upper part of the tubular insulator I3 is in direct con- ,tact with the inside of the gland nut and shield member 8thespace above the insulated-electrode and inside said insulator is kept fcoo'ler than-would otherwise be the case, as heat from "said space flows through said tubular insulator and to the wall of the gland nut andshield member and is dissipated therefrom as above explained. The

entire plug and connecter structure is therefore 'maintained at a lower temperature thanlhereto fore and, particularly, the conduction of heat from the upper end of the central electrode to the rubber insulating covering 23 of the supply cable is prevented because'of the small area of In order to secure a morecomplete dissipation of such heat as may not flow through the tubular insulating member|3 and directly to the 'plug casing as above explained heat radiating fins 33 are shown in Figure 1; the upper ends of said fins being connected together by a ring 34 which surrounds the upper'end of the gland nut and shield member 8 and is engaged .by the tubular nut l8, and the lower-ends ofwhich fins are pressed against the shell 6 of the plug: As an alternative arrangement, see Figure fiyfiiis 35 carried bya similar ring 36 contact with the member 8, instead of with the shell casing, the fins being therefore of less length than in Figure 1. It will be appreciated,however, that these fin members need to be used only in cases wherein the other features hereinbefore described for reducing plug temperature'do not reduce it as low as may be deemed desirable. Ordinarily the fin members will not need to be ,used; but their use is desirable under certain conditions which result in extremelyhigh temperatures '01. the centralelectr'ode and, being readily applicable to and remov able from the plug, they may be may be deemed necessary.

In the form of nrv'invention shown in Figure 3 the parts other than the metallic terminal conused or not as necter casing and associated parts for connecting I a supply conductor to the plug aret'he same as in Figure 1; except that the gland nut and shield member 3'! has a plurality of heat radiating fins insulator 41 which has a the central electrode 9 of the plug; and embedded corresponding with that of the supply cable 42,

which likewise has an insulating covering of rubber or like material 43 and a metallic covering or sheath 44 which is secured to the casing by a tubular nut 45 which presses a flange at the end of the sheath against a compressible packing material 46 to thereby hold the supply cable and its rubber covering in assembled relation with the casing.

Within the connecter casing 40, 4| is a moulded passage 48 in line with within the insulator is a contact member 49 having a prong SD-which enters and makes electrical connection with the stranded supply cable 42 as the same is pushed along the passage in the insulator provided for its reception, prior to securing the supply cable and its insulating covering in place by tightening the nut 45. The connecter casing is fastened to the upper end of the gland nut and shield member 3'! through a nipple depending therefrom and having a flange at its lower end, and a tubular nut 52 engaging said flange as shown. A guard 53 like the corresponding guard in the form of my invention shown in Figure 1 serves to prevent injury to the upper end of the tubular insulating member l3 when the connecter casing is removed from the plug and reassembled therewith.

In this second form of my invention a connection is established between the contact member 49 and the upper end of the central electrode 9 by a metallic rod 54 of poor heat conducting material, and of as small diameter as mechanical requirements will permit, to thereby reduce the flow of heat along said rod as much as possible; said rod having metallic caps at its ends which contact with said contact member and with the spring 32 at the upper end of the central electrode, said rod preferably having an external covering of insulating material 55. This rod extends through a packing 56 and, while it is readily removable from the connecter casing and insulator, it ordinarily comes away with the connecter casing 40, 4| when the same is removed from the plug; and it obviously serves the same purpose in substantially the same way as the wire 28 in the form of my invention illustrated in Figure l and hereinbefore described.

Having thus described and explained my invention I claim and desire to secure by Letters Patent:

1. In shielding and cooling means for spark plugs, a tubular metallic electrode supporting and shield-member adapted. to support a central electrode within a grounded plug casing; a central electrode supported by said member, and the upper end of which lies adjacent the upper end of the casing of the plug; a tubular insulating member surrounding and in contact with said central electrode and extending above the upper end thereof and terminating adjacent the upper end of said supporting and shield member, and which insulating member is in direct contact with the interior of said supporting and shield memher; a metallic connecter casing detachably secured to the upper end of said supporting and shield member; an insulator enclosed within said connecter casing; and connecting means carried by said insulator whereby and through which a conducting path may be established between a 'gh tension supply cable and the upper end of said central electrode.

2. In shielding and cooling means for spark plugs, a tubular metallic gland nut and shield member adapted to screw into a grounded plug casing; a central electrode supported by said member, and the upper end of which lies adjacent the upper end of the casing of the plug; a tubular insulating member surrounding and in contact with said central electrode and extending above the upper end thereof and terminating adjacent the upper end of said gland nut and shield mem-- her, and which insulating member is in direct contact with the interior of said gland nut and shield member; a metallic connecter casing detachably secured to the upper end of said gland nut and shield member, and which casing is made up of two parts; an insulator enclosed Within said connecter casing and having a reduced portion extending into said tubular insulating member; a yieldable gasket surrounding the reduced portion of said insulator, and which gasket is disposed between the end of said casing and the upper end of said supporting and shield member; and connecting means carried by said insulator whereby and through which a conducting path may be established between a high tension supply cable and the upper end of said central electrode.

3. In shielding and cooling means for spark plugs, a tubular metallic gland nut and shield member adapted to screw into a grounded plug casing; a central electrode supported by said member, and the upper end of which lies adjacent the upper end of the casing of the plug; a tubular insulating member surrounding and in contact with said central electrode and extending above the upper end thereof and terminating adjacent the upper end of said gland nut and shield member, and which insulating member is in direct contact with the interior of said gland nut and shield member; a metallic connecter casing detachably secured to the upper end of said gland nut and shield member; an insulator enclosed within said connecter casing; 21. wire embedded within said insulator; a terminal at one end of said wire to which a high tension supply cable may be connected; and a second terminal at the other end of said wire adapted to contact with the upper end of said central electrode.

4. In shielding and cooling means for spark plugs, a tubular metallic gland nut and shield member adapted to screw into a grounded plug casing; a central electrode supported by said member, and the upper end of which lies adjacent the upper end of the casing of the plug; a tubular insulating member surrounding and in contact with said central electrode and extending above the upper end thereof and terminating adjacent the upper end of said gland nut and shield member, and which insulating member is in direct contact with the interior of said gland nut and shield member; a metallic connecter casing detachably secured to the upper end of said gland nut and shield member; a curved insulator enclosed within said-connecter casing and extending within the tubular insulating member aforesaid to a point adjacent the upper end of said central electrode; a. wire embedded within said insulator; a terminal at one ,end of said wire to which a high tension supply cable may be connected; and a second terminal at the other end of said wire adapted to contact with the upper end of said central electrode.

5. In shielding and cooling means for spark plugs, a tubular metallic .gland nut and shield member adapted to screw into a grounded plug casing; a central electrode supported by said member and terminating adjacent the upper end of the casing of the plug, and which central electrode has an external sheath made of copper and extending throughout the length thereof; and a tubular insulating member surrounding and in contact with said central electrode and extending above the upper end thereof and terminating adjacent the upper end of said gland nut and shield member, and which insulating member is in direct contact with the interior of said gland nut and shield member.

6. In shielding and cooling means for spark plugs, a tubular metallic gland nut and shield member adapted to screw into a grounded plug casing; a central electrode supported by said member and terminating adjacent the upper end of the casing of the plug; a metallic ring at the upper end of .said gland nut and shield member; a plurality of metallic cooling fins carried by said ring and depending therefrom, and the lower ends of which fins contact with a metallic part of the spark plug structure; and a tubular insulating member surrounding said central electrode and extending above the upper end thereof and terminating adjacent the upper end of said gland nut and shield member, and which insulating member is in direct contact with the interior of said gland nut and shield member.

7. In shielding and cooling means for spark plugs, a tubular metallic gland nut and shield member adapted to screw into a grounded plug casing; a central electrode supported by said member and terminating adjacent'the upper end of the casing of the plug; a metallic ring at the upper end of said gland nut and shield member; a plurality of metallic cooling fins carried by said ring and depending therefrom, and the lower ends of which fins contact with the casing of the plug; a tubular nut at the upper end of said gland nut and shield member, and which nut engages the upper end of said ring; and a tubular insulating member surrounding said central electrode and extending above the upper end thereof and terminating adjacent the upper end of said gland nut and shield member, and which insulating member is in direct contact with the interior of said gland nut and shield member.

HECTOR RABEZZANA. 

